Automated bulk processing equipment rapidly inspects and sorts bulk articles including raw or processed fruit, vegetables, wood chips, recycled plastics and other similar products. Typically, articles are transported along a conveyor and inspected optically by means of a detection device such as a photoelectric detector. The articles can be characterized optically and sorted according to size, color, shape or other qualities. For example, stems and debris can be separated from fruit, fruit and vegetables can be reliably graded and sorted, undercooked potato chips can be distinguished and separated from fully cooked potato chips, and discolored or otherwise defective articles can be separated from acceptable articles. Elongated articles, such as carrots, french fries, and green beans, can be inspected for uniformity of size, shape, and for defects, and sorted accordingly. Modern bulk optical processing equipment can rapidly separate very large quantities of articles into many categories.
Such equipment typically includes a conveyor system that moves articles in a single layer past an inspection station where cameras or other detection devices examine the articles. The inspection station sends signals to a sorting or treatment station where the articles are sorted or otherwise treated according to information received from the inspection station. For example, foreign or defective articles may be removed from the flow of articles carried by the conveyor system. Typically, unacceptable articles are removed by directing an accurately timed blast of fluid, such as compressed air, at the article as it is projected from the conveyor belt to direct the article out of the process flow. Separation takes place at a location beyond the conveyor system where the articles are unsupported so that defective articles can easily be removed from the process flow. Acceptable articles are received in an outfeed receiving location, while unacceptable articles are directed into a reject receiving location.
Conveyor systems used for rapid inspection and sorting of large quantities of articles typically comprise a single continuous or endless conveyor belt that carries articles at speeds ranging from approximately 200 ft/min to approximately 1,100 ft/min (61 to 335 m/min). One type of conventional automated bulk processing system including a conventional conveyor and off-belt inspection system is illustrated in FIG. 1. An article infeed device 10 delivers articles to a conveyor belt 12 that moves in a direction 14 at a velocity great enough to project articles from conveyor belt 12 in a trajectory 16 toward an outfeed receiving location 18. The articles pass through an off-belt optical inspection station 20 comprising light modules 22 and 22' operably connected to a camera module 24. Unacceptable articles are removed from the flow of articles along trajectory 16 at an unacceptable article removal station by means of a fluid blast emanating from a fluid ejection manifold 26 that diverts the article in a direction 28 out of trajectory 16 and into a reject receiving location 30.
When inspecting articles off-belt for uniformity of length, width, girth, and shape, and for defects, it is important that the articles are projected from the conveyor in a single layer aligned in a particular orientation. For elongated articles, this orientation is preferably parallel to the direction of movement of the conveyor. A problem with conventional flat conveyor belt systems driven at high speeds is that the articles are delivered to the conveyor belt in random orientations and are not aligned before being projected from the conveyor. In addition, many articles are relatively unstable on the conveyor belt and tend to move laterally across the belt in addition to rolling, tumbling, bouncing and colliding with each other, resulting in misalignment of the articles as they traverse the inspection station. This misalignment makes it difficult to accurately and reliably determine the length of articles and distinguish defective articles. Singulation of the articles, i.e., separation between adjacent articles, is also important for accurate and reliable inspection. Misalignment or poor singulation of the articles also results in incorrect sorting of articles at the sorting station.
One known way to overcome these material stability problems is to provide lanes within which the articles travel as they move along in the conveyor system. An infeed device, such as a chute, a vibratory feed device, or a shaker, orients and feeds the articles into the lanes. By feeding the articles into each of the lanes in a single file manner and at intervals, the position, orientation, and singulation of the articles is maintained as the articles travel along the conveyor system.
Conventional laned sorter systems are of two types. The first is of a type comprising a wide flat belt and stationary divider walls suspended from a frame of the conveyor system and positioned above a conveying region of the flat belt to guide articles placed thereon. U.S. Pat. No. 5,515,668 describes such a system that includes adjustable dividers. This configuration is not suitable for raw food processing applications because the dividers interfere with article inspection and sorting systems, impede the flow of articles, and tend to accumulate unsanitary debris.
A second type of conventional laned sorter system includes a sorter belt having divider ribs integrally formed in or bonded to the outer surface of a flat belt. As the belt travels around the rollers at each end of the conveyor, the ribs are subjected to shear, compressive, and tensile stresses that lead to structural failure of the ribs or their bonds to the flat belt. Failure of a single rib on the belt requires the entire belt to be discarded. Although the stresses on the ribs can be reduced by increasing the diameter of the rollers, a smaller diameter roller is preferred for inspection and sorting purposes because it reduces interference of the conveyor system with the operation of the inspection and sorting system. Forming or bonding the ribs on the surface of the flat belt is expensive and requires special tooling for each lane spacing and rib height configuration used. Another disadvantage of this type of belt is that it tends to wander laterally across the rollers causing misalignment between the inspection and sorting system and the lanes, which further reduces sorting accuracy.
When processing food items, cleanliness of the conveyor system is important. Typically a conveyor belt is washed with a water spray directed onto the underside of the conveyor system then wiped dry by a squeegee blade. However, a ribbed belt is difficult to clean due to the complex topography of its surface. A squeegee cannot be used to dry the ribbed belt. Air knives can be used as a substitute for a squeegee, but are less effective than desired.
U.S. Pat. No. 5,431,289 discloses a conveyor system for aligning articles prior to inspection that comprises a plurality of lanes, each lane formed by two endless side belts separated by an endless central product-carrying belt. The side belts are raised with respect to the central product-carrying belt to define a recessed lane area for containing articles placed therein. The belts form closed loops around a pair of spaced apart rollers, one of which is a drive roller for driving the belts so that they all move at the same speed. The belts are supported by a platen that extends beneath the lanes and spans between infeed and outfeed rollers of the conveyor system. The platen includes channels routed along its length for guiding the belts and further includes lane dividers extending between adjacent lanes and above the side belts of the adjacent lanes. A cleaning system positioned beneath the platen cleans the belts as they travel about the rollers. Changing the size or spacing of the lanes in this conveyor system is difficult and expensive because it requires the platen and central product-carrying belts to be replaced. Due to its complexity, this belt and platen configuration becomes impractical for systems over 24 inches (61 cm) wide. Constant rubbing of the belts of this conveyor system across the platen tends to reduce belt life and cause premature failure of the side belts or the central belts. Failure of one of the side belts or the central belts can leave a gap in the conveyor system where articles can accumulate and jam an adjacent belt.